An inertial measurement unit (IMU) is an electronic device that measures and reports a specific force, angular rate, and sometimes the magnetic field surrounding a device. This is accomplished by using a combination of integrated circuit (IC) components, such as one or more accelerometers, gyroscopes and/or magnetometers which are mounted on a printed circuit board (PCB). IMUs measure the angular velocity and linear acceleration experienced by the IC components as they are moved. This data is sent to computer processor(s) to calculate the corresponding movement and positioning of the IMU within a field of use.
Some IMUs are configured for use with augmented reality (AR) devices and virtual reality (VR) devices, measurement devices, GPS devices, personal monitors and so forth. For an IMU to work properly, it is important for the IC components to remain securely positioned within the IMU environment, so that any detected movement of the IMU is based on movement of the device that the IMU is mounted in, as a whole, rather than any displacement of the PCB or IC components relative to one or more other components within the IMU environment.
Conventional IMU systems typically mount the PCB containing the IC components to a mounting substrate composed of one or more plastic or metal materials. The PCB is fixed in place by pins, adhesives, brackets and/or other fasteners that prevent the PCB from moving within the IMU environment. However, even when the PCB is securely mounted in place, it is still be possible for the IC components to experience relative movement within the IMU environment because of thermal expansion.
Many PCBs are manufactured out of glass-reinforced epoxy laminates, such as FR-4 or other such materials, which have a coefficient of thermal expansion (CTE) that is different than the CTE of the plastics (e.g., Liquid Crystal Polymer (LCP) substrates) and/or metals that the PCB is mounted to. During use, and depending on the types of device components and heat sinks that the IMU is used with, the ambient temperature of the IMU environment can rise more than 5°-10° C. For instance, for a AR/VR device, LEDs are used for a display engine that might generate more than 2 watts (Joules per second), various SoC components might each generate 1-2 watts, a holographic processor might generate 1-2 watts, etc.
The resulting ambient heat that is generated within an IMU during use will cause the PCB to expand or shrink at a different rate than the substrate that the PCB is mounted to. This thermal expansion can cause bowing, warping, or other displacement of the PCB, which in turn can cause linear and/or angular displacement of the IC components contained on the PCB, relative to other IC and IMU components. This is problematic because the thermal displacement can invalidate the calibration of the sensitive components and thereby introduce inaccuracies when calculating movement and positioning of the IMU during use. This can be particularly detrimental for applied uses, such as the positioning of holograms within AR/VR devices, obtaining and using measurements with precision instruments (such as laser measurement devices), and so forth.
Accordingly, there is an ongoing need to identify improved structures and methods for mounting PCBs within IMUs.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.